I have a variable of a MIP problem, for example: total_power_plants = 2.7 but I only want to use the integer part of this value, that is 2, I have been reading this article but it does not work nor is it what we need (https://how-to.aimms.com/Articles/199/199-model-rounded-variable.html#example).
Could you bring me some solution, please?
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Is the variable total_power_plants involved in other constraints ? Where is the value 2.7 coming from ?
Something like total_power_plants = sum[index_plants, power(index_plants)] ..
I believe the approach in Model a Rounded Variable — AIMMS How-To should work in your case, can you elaborate how it does not fit your needs ?
If you only need the rounded down value, you could even drop the auxilliary variable aux1 and just have var1 = value - aux2 as your constraint. Set the range of aux2 as [0,1] and the integer variable var1’s will be equal to rounddown(value).
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Looking at the variable name, I am assuming you cannot have 0.7 powerplants (it is either 0, or 1, or 2, etc).
In your case, you can set the range of the variable total_power_plants to integer and this should result in the variable only taking integer values.
Thanks for your quick response. You are right, we only can have a integer number of power plants but I can’t set the range of this variable to integer because it is calculated from the production of the plant and this variable doesn’t have to be integer.
Thanks a lot for your answer. I have changed my model and now, due to these changes, I want to have the top value of total_power_plants. I have solved it as follows:
total_power_plants_integer = total_power_plants + aux1
Where total_power_plants_integer is an integer variable and the range of aux1 is [0,1]. Generally, this solution works but when “total_power_plants” is an integer value I want to keep its value. For instance:
total_power_plants = 10
I want:
total_power_plants_integer=10
aux1=0
I tried to solve this problem changing the aux1 range: [0,1) but the solution with AIMMS was:
Warning: Postsolve indicates that solution to funciton_objetive is not reliable (see message window).
And the solution obtained does not make sense because some variables were outside their bounds.
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if you need only the roundUp value, you could even just do the below.
total_power_plants_integer >= total_power_plants
Include total_power_plants_integer to your objective function, with a minimize direction. If your problem is a minimization, then obj + total_power_plants_integer and if it is a maximization problem, then obj - total_power_plants_integer.
Regarding the “postsolve indicates solution is unreliable” warning, can you review this thread on our (deprecated) google groups forum ? https://groups.google.com/g/aimms/c/67sYx0ZHFMo/m/sUWlkLe_0dIJ
Setting the integrality option to 1 should work in most cases.
You can also review this post to improve the scaling of your model: Marcel Hunting on the AIMMS Scaling tool | AIMMS Community
+6
Hi
Hope all is well.
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